Aircraft fuel rig system fault diagnostics using digraphs

The issue of fault diagnostics is a dominant factor concerning current engineering systems. Information regarding possible failures is required in order to minimise disruption caused to functionality. A method proposed in this paper utilises digraphs to model the information flow within a system. Digraphs are comprised from a set of nodes representing system process variables or component failure modes. The nodes are connected by signed edges thus illustrating the influence, be it positive or negative, one node has on another. Fault diagnostics is conducted through a procedure of back-tracing in the digraph from a known deviating variable. A computational method has been developed to conduct this process. Comparisons are made between retrieved transmitter readings and those expected whilst the system is in a known operating mode. Any noted deviations are assumed to indicate the presence of a failure. This paper looks in detail at the application of the digraph diagnostic method to an industrially based test stand of an aircraft fuel system. Several operational phases of the system are investigated, with primary significance, with regards to system reliability, given to engine feed from the active supply tanks. This research includes transient system effects; with the rate of change of a parameter taken into consideration as a means of monitoring the system dynamically. The paper concludes with the evaluation and assessment of the validity of the results achieved.